Electrostatic condenser



-OC- 15 1929 w. DUBILIER 1,731,652.

ELECTROSTTIC CONDENSER Filed OOt. 25. 1922 Paz/yer INVENTOR BY mi@ M,)MAME/w+ LNMW A TTORNE YS Patented Oct. 15, 1929 UNITED STATES PATENTOFFICE WILLIAI DUBILIER, OF NEW YORK, N, Y., ASSIGNOR T DUBILIEBCONDENSEB COB- PORATION, A. CORPORATION OF DELAWARE ELECTROSTATIC CONDEN SER Application filed October 25, 1922. Serial No. 598,719.

bodies to a large degree many of the desirable characteristicsheretofore found only in condensers of more expensive construction.

The underlying electrical principles of the present invention are thesame as those set forth in my copending application Serial No. 472,105,filed May 24, 1921, wherein is disclosed a condenser consisting ofalternate layersl of mica and metal foil, the intermediate layers offoil being isolated one from another by the adjacent sheets of inica. Bys such a construction there is produced a oondenser capable ofwithstanding high potential and in which the tendency toward socalledbrush discharge or corona effect is greatly reduced. The brush dischargeor corona effect is that discharge which occurs as a result ofconduction alon the surfaces and thence across the edges o the sheets ofdielectric and is, in effect, a high resistance leakage. Although thebreakdown voltage 0f a condenser, as is well known,is approximatelyproportional to the thickness of the dielectric for any given dielectricmaterial, it does not follow that the brush discharge is 3o likewiseproportional. For example, an ordinary condenser comprising alternatelayers of metal foil and paper of say .002l thickness may be entirelysatisfactory and .may show no appreciable brush discharge with animpressed potential of 1000 volts. By doubling the thickness of thelayers of paper the condenser may be capable of withstanding 2000 volts,but in the latter instance an appreciable brush discharge might occur.Likewise, by tripling and-quadrupling the thickness o f the paper thebreakdown voltage may be tripled and quadrupled, but in each succeedingcase the probability of brush discharge is rapidly increasing. By theprovision of intermediate isolated or what may be termed floatingmetallic plates, the total impressed potential is divided between theseveral plates so that the potential across any one layer of dielectricis only a fraction of the total. It has been conclusively established byexperiment that the brush discharge is thus greatly decreased Withoutany increase in the amount of dielectric material required for a givencapacity and potential, as compared with condensers heretofore known.Another important advantage inherent in this type of condenser arisesfrom the fact that the flow of current therein is transverse to theplane of the metallic plates instead of parallel therewith, as in theformer type of high potential condensers, which consisted of a pluralityof serially connected condenser units. The effective ohinic resistanceof the condenser plates is therefore greatly reduced without increasingtheir thickness, and the heating effect 'is in consequencecorrespondingly small.

In high potential condensers of the ordinary type wherein two sets ofmetallic plates are separated b several layers of paper, it oftenhappens t at one or more of the layers has a defective spot in whichexcessive heat develops which, in time, burns through or causes thedisruption of the other layers of paper, whereupon the condenser breaksdown.

condenser of the ordinary type thus broken down is totally useless.Should a breakdown occur through a defective layer of dielectric betweena. pair of adjacent metallic plates in a condenser constructed inaccordance with this invention, it is not likely to be fatal. The resultof such a breakdown would, ordinarily, be merely to proportionatelyincrease the potential across the remaining layers of dielectric, and inview of the fact that condensers are usually designed with aconsiderable factor of safety, a complete breakdown would not be likelyto occur.

In accordance with the previously stated object, the present inventionprovides a condenser wliich in its preferred embodiment comprises a rollof alternate layers of liexible dielectric material such as paper, andthin sheets of conduct-ing material such as metal foil, in which theintermediate layers, or at least some of the intermediate layers offoil, are isolated. These isolated layers of foil are referred to asHoating plates, inasmuch as they are not connected to each other andhave no connecting terminal. The end or terminal plates of thiscondenser are preferably made of metal plate of suiiicient thickness andrigidity to permit their being punched or otherwise formed withsoldering terminals. These terminal plates are also preferably soproportioned that their edges extend a substantial distance beyond I theends of the roll of paper and metal foil to provide radiating surfacesfor dissipating any-heat which may be generated in the condenser. Theroll thus formed, including the terminal plates, is preferably enclosedfirst within a layer of hard fibre, which in turn is enclosed within asplit ring of spring steel or the like, and iinally within anvadjustable clamping band by which pressure may be applied to the roll.

Referring to the drawing which forms adenser pile-up.

' electric,

The condenser illustrated comprises a core 1, which in this instance isa tube of hard libre or other dielectric material, around which is wounda plurality of layers 2 of alternately interleaved sheets of paper andmetal of which the terminal layers of metal are shown in Figs. 3 and 4respectively, and comprises the outer plate 3 and inner plate 4. Theterminal plates 3 and 4 are preferably of sufiicient thickness andrigidity to permit the soldering terminals 3 and 4 being punchedintegrally therewith, whereas the intermediate plates are preferably ofmetal foil such as tin foil. These latter constitute what havebeenreferred to as the floating plates. Each of these floating plates issupported between the adjacent layers of paper, and is in no wayconnected with any of the other plates and is not provided with anyterminal for outside connection. l

In building up the condenser a sheet of paper, which is preferablyimpregnated with paraffin or other suitable impregnating diis wound onthe core 1, after vwhich plate 4 is slipped on over the layer of paper.Alternate layers of paper and metal foil are then wound about theterminal plate 4, after which the terminal plate 3 is slipped on overthe layers of paper and foil. A layer of hard fibre 5 of about 1/64thickness may then be applied around plate 3.- A split ring 6, which maysuitably be of spring steel, is placed over the layer of hard fibre, anda clamping band 7, which may also be of spring steel, encloses the ring6. The clamping band 7 has a pair of flanges 7a, 7", the former of whichis provided with two apertures of suitable siZe to pass the bolt 8, andthe latter of which is provided with apertures of -suitable size to litthe libre shouldered bushings 9. By means of the bolts 8 and their nuts10, the ends of the clamping band 7 may be tightly drawn together,thereby exerting a considerable pressure on the condenser rollcomprising the layers of metal and dielectric. The ring 6 and clampingband 7 are preferably insulated from each other by means of a coating ofshellac on their adjoining surfaces. The purpose of the insulatingbushings 9 is to interrupt the electrical continuity -of the clampingband 7, thereby reducing the possibility of excessive heat beinggenerated therein by hysteresis currents. A bracket 11, shown in Figs. 1and 2, may be electrically welded to the clamping band 7, and isprovided with an aperture 11 for mounting the condenser. The terminalplates 3 and 4 preferably extend beyond the body of the condenser, as isclearlyv shown in Figs. 2 and 5. These outwardly projecting edges of theterminal plates help to dissipate any heat which may be generated withinthe condenser.

Fig. 5 shows the condenser pile-up in perspective with the terminalplates and sheets of paper laid out flat. The floating plates, whichconsist of sheets of metal foil, are not shown in Fig. 5, as theirdimensions are such that they are hidden from view by the layers ofpaper.` The schematic diagram of Fig. 6 clearly illustrates the relationbetween the terminal plates, floating plates, and layers of paper. Inthis diagram there are shown eleven floating plates of metal foilinterposed between the terminal plates and twelve layers of dielectric.The total potential across the terminals of the condenser wouldtherefore be ldivided so that the potential across any one layer ofdielectric would be l/12 thereof.

In other words, if a potential of 1200 volts were applied to theterminals 3', 4', the potential across each layer of dielectric would be100 volts. If the thickness of each sheet of metal foil is .001, thecombined thickness thereof would amount to .011. In other words, theamount by which the thickness of the condenser is increased by insertingthe floating plates is .011, and the area of the plates is slightlyincreased to make up the loss of capacity ldue to this slight increasein separation. This slight increase in the amount of material used is,however, more than offset by the freedom from brush discharge which isobtained.

The present invention, however, is not to be construed as limited tocondensers having floating plates, as the means here described forapplying pressure to the condenser is equally applicable to rolledcondensers of the ordinary type.

I claim:

l. In an electrostatic condenser, a roll comprising alternate layers ofconducting material and non-conducting material, and adjustable meansencircling the roll and directly engaging it over virtually its wholeexterior for pressing said layers together over y substantially theirentire surface area.

2L In an electrostatic condenser, a roll comprising a plurality oflayers of dielectric material and a plurality ot' layers of conductingmaterial alternately interleaved with said layers of dielectricmaterial, certain of said layers of conducting material being adaptedfor Circuitconnections and the other or others of said layers oiconducting material being conductively isolated, and adjustable meansencircling the roll and directly engaging it over substantially itsentire eXterior for pressing and firmly holding said layers together.

3. In an electrostatic condenser', a roll comprising a plurality oflayers of dielectric material and a plurality ot' layers of conductingmaterial alternately interleaved with said layers of dielectricmaterial, Certain of said layers of conducting material being adaptedfor circuit connections and the other or others of said layers ofconducting material being con-ductively and individually isolated, aresilient split ring enveloping said roll over substantially its entireexterior, and an adjustable clamp encircling the ring to compress it andfirmly hold said layers together.

et. In an electrostatic condenser, a roll comprising alternate layers'of dielectric and conducting material, a resilient split ring,enveloping the roll over substantially its entire exterior, and aclamping band for applying pressure to the exterior of said ring forcompressing' said roll.

5. In an electrostatic condenser, a roll comprising alternate layers otdielectric and conducting material, a protecting layer of relativelystii' non-conducting material around said roll, a resilient split ringsubstantially surrounding said roll, said layer and said ring envelopingthe roll over virtually its entire extent, and a clamping band forapplying pressure to the exterior of said ring for compressing saidroll.

In testimony whereof I atX mV signature.

WILLIAM DU'BILIER.

